There are many situations where it is therapeutically desirable to increase the amount of tear fluid produced by the eye. Dry eye disease is the general term for indications produced by abnormalities of the precorneal tear film characterized by a decrease in tear production or an increase in tear film evaporation, together with the ocular surface disease that results. Approximately 38 million Americans are affected with some type of dry eye disorder. Among the indications that are referred to by the general term “dry eye disease” are: keratoconjunctivitis sicca (KCS), age-related dry eye, Stevens-Johnson syndrome, Sjogren's syndrome, ocular cicatrical pemphigoid, blepharitis, corneal injury, infection, Riley-Day syndrome, congenital alacrima, nutritional disorders or deficiencies (including vitamins), pharmacologic side effects, eye stress and glandular and tissue destruction, environmental exposure to smog, smoke, excessively dry air, airborne particulates, autoimmune and other immunodeficient disorders, and comatose patients rendered unable to blink. The present invention may also be useful as a wash or irrigation solution in conscious individuals, during surgery or to maintain comatose patients or those who cannot blink due to neuromuscular blockade or loss of the eyelids.
A healthy precorneal tear film has several important functions: 1) to protect the cornea from desiccation; 2) to aid in the immune response to infections; 3) to enhance oxygen permeation into the cornea; 4) to allow gliding movement of the eyeball and eyelids; and 5) to help maintain the ocular pressure through osmosis. There are two structures responsible for maintaining the properties of the tear film—the lacrimal glands and the conjunctiva (the mucous membrane which surrounds part of the eyeball and inner eyelids). These structures maintain the tear film via regulation of water and electrolyte transport and via mucin release by goblet cells.
The progression of dry eye disease is characterized by four main “milestones.” The first milestone is a decrease in tear production. In rabbit models, this decrease in tear production has been shown to correlate with an increase in tear osmolarity. The second milestone is a loss of mucous-containing conjunctival goblet cells. This decrease in goblet cell density becomes evident several weeks after the onset of decreased tear production. The third milestone in the progression of dry eye disease occurs about 1 year later when desquamation of the corneal epithelium is observed. The fourth and last milestone of the disease is a destabilization of the cornea-tear interface (J. Gilbard, CLAO Journal 22(2), 141-45 (1996)).
Currently, the pharmaceutical treatment of dry eye disease is mostly limited to administration of artificial tears (saline solution) to temporarily rehydrate the eyes. However, relief is short-lived and frequent dosing is necessary. In addition, artificial tears often have contraindications and incompatibility with soft contact lenses (M. Lemp, Cornea 9(1), S48-550 (1990)). The use of phosphodiesterase inhibitors, such as 3-isobutyl-1-methylxanthine (IBMX) to stimulate tear secretion is disclosed in U.S. Pat. No. 4,753,945 (applicant intends this and all other patent references to be incorporated herein). The effectiveness of these phosphodiesterase inhibitors is currently being investigated (J. Gilbard, et al., Arch. Ophthal, 112, 1614-16 (1994) and 109, 672-76 (1991); idem, Inv. Ophthal. Vis. Sci. 31, 1381-88 (1990)). Stimulation of tear secretion by topical application of melanocyte stimulating hormones is described in U.S. Pat. No. 4,868,154.
There are many situations where it is therapeutically desirable to increase drainage of the lacrimal system. The lacrimal system has two functioning components: the secretory part, which produces tears, and the excretory part, which drains the tears into the nose. When the lacrimal drainage system is not functioning properly the result can be excessive tearing (epiphora), mucopurulent discharge, and recurrent dacryocystitis (C. Shermataro, et, al., JAOA, 94, 229 (1994)). In fact, tearing is one of the most common complaints that brings a patient to the ophthalmologist's office (S. T. Conway, Ophthal. Plas. Reconstr. Surg., 10, 185 (1994)).
The most common malfunction of the lacrimal drainage system is nasolacrimal duct obstruction, which results in stasis of tears in the lacrimal sac. The accumulation of fluid and mucus results in tearing and expulsion of mucopurulent material, causing the eyelids to be “stuck together” on awakening in the morning. The lack of clearance of the tear fluid also leads to inflammation and chronic infection of the lacrimal sac and ducts (K. J. Hyde, et, al., Ophthal., 95, 1447 (1988); J. A. Blicker, et. al., Ophthal. Plas. Reconstr. Surg., 9, 43 (1993); J. A. Mauriello Jr., et. al., Ophthal. Plast. Reconstr. Surg., 8, 13 (1992)).
Nasolacrimal duct obstruction can be divided into two etiologic classes: primary acquired nasolacrimal duct obstruction (PANDO), which is characterized by hyperplasia and fibrosis of the mucosal epithelium, and secondary acquired nasolacrimal duct obstruction (SANDO), which is caused by cancer, inflammation, infection, trauma and mechanical problems (G. B. Bartley, Ophthal. Plast. Reconstr. Surg., 8, 237 (1992)). An occluded nasolacrimal duct is more common in middle-aged women and infants. In fact, up to 20% of all infants are affected by nasolacrimal duct obstruction with most of them becoming symptom free by their first birthday (J. D. H. Young, et. al., Eye, 10, 485 (1996)).
Current treatments for nasolacrimal duct obstruction are mostly invasive or surgical procedures that vary in aggressiveness. Intervention can take the form of probing the duct with a fine catheter; however, this is a difficult and delicate procedure that requires special training and equipment (J. Kassoff, et. al., Arch. Ophthal., 113, 1168 (1995); J. D. Griffiths, U.S. Pat. No. 4,921,485 (1990) and U.S. Pat. No. 5,062,831 (1991); B. B. Becker, et. al., U.S. Pat. No. 5,021,043 (1991) and U.S. Pat. No. 5,169,386 (1992)). In some cases silastic intubation of the nasolacrimal duct increases drainage of tears through the nasolacrimal duct (R. K. Dortzbach, et. al., Amer. J. Ophthal., 94, 585 (1982); H. Al-Hussain, et. al., Ophthal. Plas. Reconstr. Surg., 9, 32 (1993); J. S. Crawford, et. al. U.S. Pat. No. 4,380,239 (1983); W. L. Ector, Jr., U.S. Pat. No. 4,658,816 (1987)). A more aggressive procedure is a dacryo-cystorhinostomy which surgically creates a new drainage path above the sight of obstruction allowing continuity between the lacrimal sac and the nasal cavity (J. V. Linberg, et. al., Ophthal., 93, 1055 (1986); K. J. Tarbert, Ophthal., 102, 1065 (1995); F. E. O'Donnell, Jr., U.S. Pat. No. 5,345,948 (1994)). External massage of the nasolacrimal duct has also been shown to increase tear transit times through the nasolacrimal duct (J. A. Foster, et. al., Ophthal. Plas. Reconstr. Surg., 12, 32 (1996)).
Thus, as a result of the ineffectiveness and inconvenience of current therapies, medical researchers have sought to develop alternatives for the treatment of dry eye disorders and nasolacrimal duct disorders. It has been shown that uridine 5′-triphosphate (UTP) and adenine 5′-triphosphate (ATP) are potent agonists of P2Y2 purinergic receptors found on the surface of human airway epithelium. Activation of these P2Y2 purinergic receptors induces chloride and water secretion, helping hydrate the airway surface secretions. Use of UTP and ATP for the purpose of treating pulmonary disorders characterized by the retention of lung mucus secretions is described in U.S. Pat. No. 5,292,498, Because of the demonstrated ability of UTP to increase hydration of airway epithelial secretions, applicants were motivated to investigate whether UTP and other P2Y2 and P2Y4 purinergic receptor agonists could also stimulate hydration of ocular epithelia. It had previously been shown that P2 type purinergic receptors in rat and mouse lacrimal acinar cells responded to extracellular ATP by increasing intracellular calcium (I. Sasaki, et al., Febs Lett. 264, 130-34 (1990); idem, J. Physiol. 447, 103-18 (1992); P. Vincent, J. Physiol. 449, 313-31 (1992); J. Gromada, et al., Eur J. Physiol. 429, 578 (1995); V. Lee, et al. Inv. Ophthal. Vis. Sci. 38(4)(1997) abstract). Applicant has discovered that tear secretion can be stimulated from lacrimal accessory tissues via P2Y2 and/or P2Y4 purinergic receptor-mediated mechanisms similar to those which hydrate airway epithelia. Applicant has also discovered that stimulators of mucociliary clearance when applied topically to the eye or injected into the nasolacrimal drainage system increases the flow of tears through the nasolacrimal duct and hence relieves the symptoms associated with nasolacrimal duct obstruction. UTP and other purinergic receptor agonists, administered topically or systemically, provide a novel method of treating dry eye disorders and nasolacrimal duct obstruction.